JP4925007B2 - Method for producing piezoelectric spherical fine particles - Google Patents

Description

  The present invention relates to a method for producing piezoelectric spherical fine particles that can be suitably used as a raw material powder for a piezoelectric body.

Pb (Zr _x , Ti _1-x ) O ₃ (hereinafter referred to as PZT) is one of the most representative ferroelectrics, and recently in the field of MEMS (Micro Electro Mechanical System), a microsensor. Application as a microactuator has been actively studied. Therefore, typical processes for thick film fabrication (> 10 μm), such as electrodeposition and screen printing, are based on particle arrangement, filling, and sintering on the element substrate, which can be used for miniaturization and integration of devices. Along with this, the properties of the individual particles have become extremely important.

  Conventional methods for producing piezoelectric fine particles include a solid phase method, a liquid phase method, and a gas phase method.

  Among these, spray pyrolysis (Non-Patent Document 1), sol-gel method, and the like have been reported as methods for producing spherical fine particles.

  However, the spray pyrolysis method basically uses an inorganic salt such as nitrate containing a metal element as a raw material, an organic salt such as acetate, or an organic metal compound such as metal alkoxide in water or alcohol. This is a method in which a dissolved solution is used as a raw material and sprayed into a reaction vessel kept at a high temperature to perform thermal decomposition. Spheroidization is possible by controlling the solution spraying method, thermal decomposition temperature, solution concentration, etc., but the solution concentration is typically limited to about 0.0X mol / L, so it is difficult to increase the yield. There is a disadvantage that time is required. In addition, there is a drawback that the burden on the environment is large, such as the generation of a large amount of gas due to thermal decomposition and combustion of solvents such as raw material salts and alcohol.

  Also, the sol-gel method has a disadvantage in terms of price because, like the spray pyrolysis method, a metal alkoxide or the like is used as a raw material, and the raw material is relatively expensive and difficult to handle. In addition, these raw materials are used as a solution once dissolved in water, alcohol, or various organic solvents, and the solution concentration is relatively low due to the solubility of the raw materials and the stability of the solution. .

  As another method for producing piezoelectric fine particles, a molten salt method is known.

  In the molten salt method, particles with various forms such as plates and needles can be synthesized at a relatively low temperature and in a short time, accompanied by dissolution and precipitation reactions of the raw material components in the molten inorganic salts (flux). Has been reported.

  The advantages of the molten salt method compared to the spray pyrolysis method and the sol-gel method described above are that metal oxide powder is used as a relatively inexpensive and more stable raw material, and this is used as a stable material such as chloride or fluoride. Ceramic fine particles can be produced by a molten salt reaction by heating with salts (flux). Furthermore, the reaction product cooled to room temperature after heating and melting can be washed with water and filtered to recover the piezoelectric fine particles, and the salts used at this time are basically recyclable. is there.

By the way, the technique of adding PbO excessively at the time of PZT manufacture is known, and it is used well irrespective of the kind of manufacturing method. In this method, when the heating temperature is about 800 ° C. or higher, defects due to evaporation of PbO from PZT become conspicuous as the temperature rises. Excessive addition of PbO is originally intended to compensate for the evaporation of PbO, and it is known that a similar method is used when producing PZT particles by the molten salt method.
Osamu Sakurai, others, Journal of the Ceramic Society of Japan, Vol.97, No.4, 1989, P407-12

  However, in the conventional molten salt method, although there are advantages relating to the production such that a relatively inexpensive and more stable raw material can be used, an aggregate of irregularly shaped fine particles can be produced with respect to PZT. Currently, spherical particles are not obtained.

  In the process of thick film production by the above-described electrodeposition method or screen printing method, particle arrangement / filling / sintering on the element substrate is fundamental, and the properties of the individual particles become smaller as devices become smaller and more integrated. It has become extremely important. Spheroidization and refinement of particles are representative of the most important factors for the close packing of particles and improvement of sinterability. Therefore, for such reasons, a technique for producing spherical PZT fine particles with high efficiency is desired.

  Accordingly, the present invention has been made to solve the above problems, and its purpose is to provide a method for producing spherical piezoelectric fine particles using a molten salt method that is excellent in recyclability and mass productivity. It is to provide.

  The inventor of the present application adjusts the type and composition of the raw material powder and salts (flux) used in the molten salt method, and after mixing, heat-reacts under an appropriate temperature condition, The inventors have found that production is possible, and have completed the present invention.

  That is, in order to solve the above-described problem, the manufacturing method according to the present invention mixes and heats an oxide as a main raw material of piezoelectric fine particles with molten inorganic salts that cause a molten salt reaction with the oxide. A method for producing piezoelectric fine particles for producing piezoelectric fine particles, wherein a predetermined amount of lead oxide (PbO) is mixed with the oxide together with the oxide and the molten inorganic salt and heated at a predetermined temperature. It is characterized by.

The manufacturing method according to the present invention, the oxide and together with the lead oxide, it is preferable to mix a predetermined amount of lead chloride (PbCl ₂₎ with respect to the oxide.

The manufacturing method according to the present invention, as the _{oxide, Pb (Zr x, Ti 1} -x) O 3 (X shows 0-1) is preferably used.

  In the manufacturing method according to the present invention, the predetermined temperature is preferably in the range of 700 ° C to 1100 ° C.

  Moreover, it is preferable that the manufacturing method which concerns on this invention uses the said lead oxide in 1-30 mass% with respect to the said oxide.

  Moreover, it is preferable that the manufacturing method which concerns on this invention uses the said lead chloride in the range of 30 mass% or less exceeding 0 with respect to the said molten inorganic salt.

  Moreover, it is preferable that the manufacturing method which concerns on this invention mixes the said oxide 50-75 mass% with respect to the said molten inorganic salt.

  In the production method according to the present invention, a mixed salt of potassium chloride and lithium fluoride is preferably used as the molten inorganic salt.

  In the manufacturing method according to the present invention, the first mixture obtained by mixing the lead oxide and the oxide and the second mixture obtained by mixing the molten inorganic salt and the lead chloride are prepared, and then the first mixture is prepared. It is preferable to mix the mixture and the second mixture.

  In order to solve the above problems, the piezoelectric fine particles according to the present invention are manufactured by the above manufacturing method.

  The piezoelectric fine particles are preferably spherical.

  In order to solve the above-described problems, the device according to the present invention is manufactured using the piezoelectric fine particles manufactured by the above-described manufacturing method and the above-described piezoelectric fine particles.

  The manufacturing method according to the present invention, as described above, manufactures piezoelectric fine particles by mixing and heating an oxide as a main raw material of piezoelectric fine particles with molten inorganic salts that cause a molten salt reaction with the oxide. A method for producing piezoelectric fine particles is characterized in that a predetermined amount of lead oxide (PbO) is mixed with the oxide in the molten inorganic salt together with the oxide and heated at a predetermined temperature. In addition, the piezoelectric fine particles according to the present invention are manufactured by the above manufacturing method.

  According to said method, the liquid phase containing the said lead oxide obtained by adding lead oxide is the viscosity of molten inorganic salt (molten flux), and the ion (for example, PZT constituent ion) which comprises an oxide. A change in physical properties such as a diffusion coefficient affects the production mechanism of the piezoelectric fine particles, and it becomes possible to produce piezoelectric fine particles (particle size: about 0.05 to 3 μm) having excellent dispersibility.

  Also, according to the above method, spherical piezoelectric fine particles can be obtained even by a molten salt method excellent in recyclability and mass productivity.

[1] Method for Producing Piezoelectric Fine Particles The inventors of the present invention adjust the type and blending composition of raw material powders and salts (flux) used in the molten salt method, and after mixing, heat-react under an appropriate temperature condition. Thus, the above problem is solved by providing a method for producing piezoelectric spherical fine particles by the same method. Among these, the liquid phase containing PbO, which is considered to be generated especially when PbO is excessively added, affects the formation mechanism of PZT fine particles due to changes in physical properties such as the viscosity of the melt flux and the diffusion coefficient of PZT constituent ions. As a result, a method that focuses on forming spherical fine particles having excellent dispersibility has not been known so far.

In the present invention, in order to generate the liquid phase containing PbO at a lower temperature, the more effective flux composition and the effect of adding PbCl ₂ were studied together, and appropriate production conditions were found.

  Hereinafter, although one Embodiment of this invention is described, the scope of the present invention is not limited to this.

In this embodiment, PbO, ZrO ₂ , and TiO ₂ metal oxide powders are used as starting materials, and Pb (Zr _x , Ti _1-x ) O ₃ (X represents 0 to 1) (hereinafter, Compared to the stoichiometric composition of PZT), an excessive amount of PbO is added within a certain range, and further PbCl ₂ is added within a certain range, and mixed together with an inorganic salt (flux) such as KCl, NaCl, or LiF. Thereafter, a heated molten salt reaction is caused.

  As the starting material, in addition to the above metal oxides, carbonates, nitrates, oxalates, acetates, hydroxides, organic salts, or organic metal compounds that can be easily converted to these oxides by heating, What changes to these oxides by heating can be illustrated.

  Such oxides typically have a valence of 1 such as alkali metal ions, alkaline earth metal ions, rare earth ions, transition metal ions, etc., in accordance with the intended function and characteristics of the piezoelectric body. It is possible to include various dopant elements having ionic radii ranging from valence to hexavalence. The dopant element may be a combination of a plurality of dopant elements.

  The inorganic salt may be any substance that melts at about 1000 ° C. or less and causes a molten salt reaction with the PZT raw material powder, such as chloride, sulfide, fluoride, and the like. It may be. Specifically, a mixed salt obtained by mixing potassium chloride (KCl) and lithium fluoride (LiF) at a molar ratio of 80:20 is preferable.

  As addition amount of PbO, it is preferable to add 1-20 mass% with respect to PZT stoichiometric composition, 3-15 mass% is more preferable, and 5-10 mass% is further more preferable.

Also, when adding PbCl _2, compared melt flux, it is preferable to add a 30 wt% more than 0, more preferably from 3 to 15 wt%, more preferably about 10 wt%.

  About the mixing ratio of PZT raw material powder and a flux, what is necessary is just to mix so that PZT raw material powder may be 10-95 mass%, 25 mass% or more is preferable and 50-75 mass% is the most preferable.

In this embodiment, PZT raw material powder, PbO, and PbCl ₂ are added to a flux, mixed, and heated to cause a heated molten salt reaction.

  As the heating temperature, spherical PZT particles are obtained in the range of 750 to 1100 ° C., and smaller particles are obtained when the heating temperature is lower. In particular, spherical and finer particles can be obtained at temperatures around 800 ° C.

  Regarding the heating time, the longer the heating and holding time, the larger the particles tend to be. In order to obtain smaller and spherical particles, the heating and holding time of about 30 to 60 minutes is optimal at the above heating temperature. is there.

  Cool after heating. Cooling may be natural cooling.

  The heating rate and the cooling rate are not significantly affected by the size of the PZT particles, but can be set to 10 ° C./min, for example, but may be set according to the situation.

  As described above, according to the production method of the present invention, compared to the conventional method, the oxide raw material powder is cheap and stable, and the advantages of the molten salt method are the recyclability and the mass productivity. And fine particles having a particle shape close to a sphere and relatively small cohesiveness (particle size: about 0.05 to 3 μm) can be obtained more efficiently.

  Specific characteristics of the piezoelectric fine particles obtained by the above-described method will be described in Examples described later.

[2] Utilization of Piezoelectric Fine Particles Since the piezoelectric fine particles produced by the above method are spherical, the piezoelectric fine particles of this embodiment can be suitably used for devices such as microsensors and microactuators.

  Specifically, in the above-described thick film manufacturing process, it is used as a raw material powder of a piezoelectric body, and can be used as a raw material having excellent filling properties and excellent sinterability. Moreover, it is also suitable as a sintering raw material for bulk products such as general piezoelectric sensors and ultrasonic vibrators.

  The invention is illustrated in more detail by the following examples, but should not be limited thereto.

(A) Production of Piezoelectric Fine Particles The present inventors produced piezoelectric fine particles using the above-described production method.

The PZT mixed powder was weighed so that the composition ratio of lead oxide (PbO), zirconia oxide (ZrO ₂ ), and titanium oxide (TiO ₂ ) was 1: 0.57: 0.43 in molar ratio, respectively. Wet ball mill mixing was performed in ethanol using _two balls. And what mixed was fully dried at 110 degreeC was used.

Next, this PZT mixed powder was mixed with flux, PbCl ₂ , and PbO excess. As the flux, KCl and LiF were used and weighed so that the molar ratio was 80:20. The mixing ratio of the PZT mixed powder and the flux was changed from 5:95 to 95: 5 (weight ratio). This ratio was typically 50:50 (weight ratio) unless otherwise specified. The amount of PbO added was the amount shown in FIG. 1 in the range of 0 to 15% by mass (wt%) with respect to the PZT mixed powder. The amount of PbCl ₂ added was the amount shown in FIG. 2 in the range of 0 to 15 mass% (wt%) with respect to this flux. All the mixing was performed by wet ball mill mixing (about 17 hours) in ethanol using ZrO ₂ balls and sufficiently dried.

  After drying, the mixture was transferred to a platinum (Pt) crucible and heated in an electric furnace in the range of 600 to 1100 ° C. for 1 hour at each temperature shown in FIG. The heating rate was 10 ° C./min, and cooling was performed by natural cooling (furnace cooling) in an electric furnace.

  The sample thus obtained was washed with distilled water at about 80 ° C. by decantation a dozen times, filtered and dried to obtain PZT spherical fine particles.

FIG. 1 shows how the shape of the PZT spherical fine particles differs depending on the difference in the amount of PbO added when the above-mentioned PZT mixed powder, flux, and 10 mass% PbCl ₂ are used. The result verified based on the SEM image is shown. In this experiment, heating was performed at 950 ° C.

  FIG. 1 shows that the particles were spheroidized when the amount of PbO added was 5 to 10% by mass.

Next, FIG. 2 shows how the shape of PZT spherical fine particles varies depending on the difference in the amount of PbCl ₂ added when the above-described PZT mixed powder, flux, and 5 mass% PbO are used. The result verified based on the SEM image of spherical fine particles is shown. In this experiment, heating was performed at 950 ° C.

FIG. 2 shows that spheroidization of PZT fine particles progressed when the amount of PbCl ₂ added was around 3 to 10% by mass.

Next, FIG. 3 and FIG. 4 show the results of verifying the difference in the shape of the PZT fine particles and the crystal phase due to the difference in heating temperature. FIG. 3 is an SEM image of PZT spherical fine particles, and FIG. 4 shows the result of measuring the change in crystal phase of PZT spherical fine particles by powder X-ray diffraction. In this experiment, heating was performed for 1 hour, and 10 mass% PbCl ₂ and 5 mass% PbO were added.

  FIG. 3 shows that the PZT fine particles are spheroidized when the heating temperature is 800 ° C. or higher. Further, from FIG. 4, when the heating temperature was 750 ° C. or higher, PZT fine particles were formed (peaks indicated by ◯ in FIG. 4), but a small amount of unidentified phase was observed as a by-product (× Peak). In addition, this by-product was able to be removed by the process which is immersed and stirred for about several hours in the acetic acid aqueous solution.

Next, FIG.5 and FIG.6 shows the result of having verified about the difference of the shape of a PZT microparticles | fine-particles by the difference in the PZT mixed powder density | concentration with respect to a flux, and a crystal phase. FIG. 5 is an SEM image of PZT spherical fine particles, and FIG. 6 shows the results of measuring the change in crystal phase of PZT spherical fine particles by powder X-ray diffraction. In this experiment, 10% by mass of PbCl ₂ was added, flux and 5% by mass of PbO were added to each concentration of PZT mixed powder, and heating was performed at 850 ° C. for 1 hour.

  FIG. 5 shows that PZT spherical fine particles are obtained when 50 to 70% by mass of PZT mixed powder is mixed with respect to the flux. Further, in FIG. 6, PZT fine particles were formed when the PZT mixed powder was 10% by mass or more with respect to the flux (peaks indicated by ◯ in FIG. 6), but as in the result of FIG. Was observed (peak indicated by x in FIG. 6). This by-product could also be removed by a process of immersion and stirring for about several hours in an aqueous acetic acid solution.

It can be said that the present invention is characterized by the following configuration. That is, the first feature of the present invention is that it is a method for producing piezoelectric particles made of Pb (Zr _x , Ti _1-x ) O ₃ (X represents 0 to 1). Furthermore, with respect to the first feature, various alkali metal ions, alkaline earth metal ions, rare earth ions, transition metal ions, etc., having various ionic radii from 1 to 6 valences, It is preferable that a dopant element is included. Moreover, it is preferable that it is a manufacturing method of the PZT piezoelectric particle containing various combinations of said dopant. Regarding the first feature, it is preferable that the piezoelectric body contains various dopant elements. Moreover, regarding the first feature, it is preferable that the method is a method for producing PZT piezoelectric spherical fine particles. Regarding the first feature, it is preferable to use various inorganic salts such as KCl and LiF as the flux and add an excess amount of PbO to PZT.

(B) Production of sintered body and characteristics of the sintered body A sintered body was produced using the particles obtained in the above (A), and the evaluation of the sinterability and the electrical characteristics were analyzed.

  For the production of a sintered body for measuring electrical characteristics, PZT spherical fine particles synthesized under the condition that fine particles having the most spherical shape and excellent dispersibility were used. As specific synthesis conditions, the kind of flux, concentration, and PbO excess addition amount are the same as those shown in FIG. The heating temperature was 800 ° C.

  The particles obtained in the above (A) were uniaxially pressed at 98 MPa in a disk shape having a diameter of about 15 mm and a thickness of about 1 mm using a mold. A small amount of 3% PVA aqueous solution was added as a molding aid. The obtained compact was degreased in an electric furnace at 600 ° C. for 1 hour in air, then placed in a MgO crucible covered with platinum foil, and in an electric furnace at 1200 ° C. to 1300 ° C. for 1 hour in air. Was sintered to obtain a sintered body.

(Evaluation of sinterability)
The bulk density of the sintered body was measured by the Archimedes method using water and expressed as a relative density with respect to the theoretical density (8 g / cm ³ ).

[Electrical measurement]
A silver paste was applied to the surface of the sintered body and baked at 600 ° C. to form an electrode. The sample was polarized by applying a 3 kV / mm direct current electric field in silicon oil heated to 80 ° C. for 30 minutes.

  The electromechanical coupling coefficient (Kp) of the sample was measured by a resonance-antiresonance method using an impedance analyzer.

  Moreover, the dielectric constant in 1 kHz was measured using the same apparatus as the above.

The piezoelectric strain constant (d ₃₃ ) was measured using a d ₃₃ meter.

[Results and discussion]
FIG. 7 shows the relationship between the sintered body density and the sintering temperature. Regarding the sinterability of the particles obtained in the above (A), the relative density is increased to 96.1% (when sintered at 1200 ° C.) and 97.6% (when sintered at 1300 ° C.), and is easily baked. It was found to have cohesiveness.

  Table 1 shows the measurement results for typical electrical characteristics. In Table 1, as an index of practicality, Non-Patent Document 2 (“Ferroelectric Materials and Their Applications”, Yuhuan Xu, North-Holland, Elsevier Science Publishers BV, 1991, pp. 131) and Non-Patent Document 3 ( The characteristic values of the sintered body described in Ceramic Dielectric Engineering, Kiyoshi Okazaki, Gakudensha, 3rd edition, 1983, pp.334) are also shown as literature values.

The value of the electromechanical coupling coefficient (Kp), which is the most important index of piezoelectricity, tended to increase as the sintering temperature was increased, but the same value as the literature value was obtained overall. Further, it was found that the piezoelectric strain constant (d ₃₃ ) increases with an increase in the sintering temperature, and a characteristic value superior to the literature value can be obtained. The dielectric constant was almost the same as the literature value.

  Here, the sintered bodies of Non-Patent Documents 2 and 3 are basically sintered using piezoelectric particles produced by a method called a solid-phase reaction method, basically the sintering method performed in this example. Sintered by the same method as above. The solid phase reaction method is the most representative method for producing ceramic raw material powders industrially. Oxide or carbonate raw material powder is used as a starting material, weighed a specified proportion, then mixed well by a mechanical method using a ball mill or the like, and calcined at a temperature range of about 700 ° C to 1000 ° C. . Here, once the target PZT crystal phase is generated, mechanical pulverization is performed again using a ball mill or the like. In addition to the complexity of the process for producing the raw material powder particles, it is generally difficult to produce particles having a particle size of 1 μm or less by such a solid-phase reaction method. Problems such as large distribution are also known.

  On the other hand, compared with the solid-phase reaction method, the present invention is based on a method called a molten salt method in which various factors such as the effect of excessive addition of PbO and the kind of flux, blending ratio, and heating conditions are optimized. There is an advantage that spherical fine particles having a particle diameter of about 0.05 to 3 μm can be directly synthesized, and the synthesized particles are molded and sintered as they are, and are 96% of the theoretical density even at a relatively low temperature of 1200 ° C. Densification can be achieved up to the above, and a material having the same electrical characteristics as the literature value can be easily produced. In addition, the thing of literature value was sintering temperature 1280-1290 degreeC.

  According to the production method of the present invention, spherical piezoelectric fine particles can be produced using a molten salt method excellent in recyclability and mass productivity.

  Therefore, the piezoelectric fine particles produced by the above production method can be suitably used for devices such as microsensors and microactuators.

It is the SEM image of the PZT spherical fine particle which verified the particle shape change by the difference in the addition amount of PbO about the piezoelectric fine particle manufactured by the method of this invention. It is a SEM image of the PZT spherical fine particle which verified the particle shape change by the difference in the addition amount of PbCl ₂ about the piezoelectric fine particle manufactured by the method of the present invention. It is the SEM image of the PZT spherical fine particle which verified the particle shape change by the difference in heating temperature about the piezoelectric fine particle manufactured by the method of this invention. It is the graph which verified the change of the crystallinity of the particle | grains by the difference in heating temperature about the piezoelectric fine particle manufactured by the method of this invention. It is a SEM image of the PZT spherical fine particle which verified the particle shape change by the difference in the PZT mixed powder density | concentration with respect to the flux about the piezoelectric fine particle manufactured by the method of this invention. It is the graph which verified the change of the crystallinity of the particle | grains by the difference in the PZT mixed powder density | concentration with respect to the flux about the piezoelectric fine particle manufactured by the method of this invention. It is the figure which showed the relationship between the sintering temperature of the piezoelectric fine particle manufactured by the method of this invention, and a sintering density.

Claims (5)

A method for producing piezoelectric fine particles, in which an oxide that is a main raw material of piezoelectric fine particles is mixed with heated inorganic inorganic salts that cause a molten salt reaction with the oxide to produce piezoelectric fine particles,
As the oxide, Pb (Zr _x , Ti _1-x ) O ₃ (X represents 0 to 1) is used.
The oxide with respect to 3 to 10 wt% of lead oxide (PbO), was mixed on SL molten inorganic salts, and 50 to 75 wt% of the oxide with respect to the molten inorganic salts, the mixture 800 ° C. The manufacturing method characterized by heating at the above temperature. The manufacturing method according to claim 1, wherein a predetermined amount of lead chloride (PbCl ₂ ) is mixed with the oxide and the lead oxide together with the oxide. The manufacturing method according to claim 2, wherein the lead chloride is used in a range of more than 0 to 30% by mass or less with respect to the molten inorganic salt. The production method according to any one of claims 1 to 3, wherein a mixed salt of potassium chloride and lithium fluoride is used as the molten inorganic salt. After making the 1st mixture which mixed the said lead oxide and the said oxide, and the 2nd mixture which mixed the said molten inorganic salt and the said lead chloride, the said 1st mixture and the 2nd mixture are mixed. The manufacturing method of Claim 2 characterized by these.